The present invention relates generally to pipe or tube fluid fittings such as miniature 2, 3 or more port branch connectors, and more particularly to the manufacture of the same from a metal billet or stock, such as a plate or barstock, having the potential for one or more centerline inhomogeneities.
Fittings of the type herein involved are well known as employed in a variety of applications to connect two or more runs of tubing, pipes, lines, or other conduits in fluid communication at a central junction. In basic construction, such fittings typically are formed from a metal such as copper, brass, steel, or stainless steel as a pressure vessel having two or more branches or bosses for mechanical or fusion coupling to the ends of the conduits to be joined. Depending upon the number and relative orientations of the branches, two port elbows and other configurations such as tees or crosses having three or more ports may be provided.
Recently, applications in the semiconductor and other electronics markets have dictated "miniaturized" fittings having port diameters of from about 1/8 to 1-inch and various wall thicknesses. Conventionally, these fittings are machined, for example, from a 5/8-inch by 5/16-inch by 7/8-inch or similarly proportioned slug or blank sectioned from a length of a rectangular section metal barstock. In forming the barstock, molten metal such as steel is cast into a crucible or the like for solidification into a generally cylindrical ingot or billet. The solidified billet, in turn, is extruded, forged, rolled, drawn, or otherwise worked into an elongate barstock of a typically polygonal cross-section configured for the machining of the fitting therefrom with a minimum amount of wasted material.
It is known that contraction during the directional solidification of the billet results in the preferential concentration of inhomogeneities such as impurities, inclusions, occlusions, voids, or other defects within a "pipe" or core that extends along the longitudinal, i.e., axial, centerline thereof. As the billet is worked to reduce its cross-section, the inhomogeneities are propagated as "stringers" along the central longitudinal axis of the resulting barstock and, in turn, along the centerline of each of the blanks sectioned therefrom. If one of these centerline inhomogeneities intersects a wall or other pressure boundary of the fitting, the likelihood that the fitting will fail prematurely in service is increased. A defect rate even as low as about 0.1%, however, is considered unacceptable for ultra high purity gas or other critical applications.
Proposals have been made for methods of manufacturing fittings and for reducing centerline defects in billets. For example, U.S. Pat. No. 942,489 discloses a method of removing the "pipe" from an ingot for producing wrought articles that are free from flaws. The method entails passing a heated ingot through a set of rollers in a rolling mill that are provided with flanges. The roller flanges effect the separation of the contaminated central portion of the ingot from between a pair of relatively defect-free, surrounding outer portions.
U.S. Pat. No. 1,987,201 discloses a method of making seamless tubing via the centrifugal casting of an ingot in a cylindrical, rotating mold. The centrifugal force that is developed during the solidification of the ingot concentrates any impurities, voids, or other defects along the longitudinal axis of the ingot. A hole then is bored longitudinally through the axial center of the ingot prior to the rolling thereof for removing the contaminated area within which the defects have been concentrated.
U.S. Pat. No. 2,074,712 discloses a method of making welding rods from a steel ingot having a contaminated central "pipe" portion and a purer rim portion. The ingot is rolled for its reduction into a flattened strip or plate so as to expand the rim section at the edges of the resulting strip. The edge then may be removed by a slitting operation as strands that are cut from the strip.
U.S. Pat. No. 2,115,893 discloses a method of coring and dividing steel ingots for removing the defective core portion thereof. The ingot is cast in a conventional manner in a cruciform cross-section, and then is placed between a die structure having a similar but slightly larger cruciform cross-section. A punch having a cross-section substantially equal to the cross-section bounded by the arms of the die structure is driven lengthwise through the ingot removing the defective core portion and filling the arms of the die structure with the remaining metal of the ingot. The reference notes that it had been known to remove the defective core portion of a steel or other metal ingot by dividing the ingot along the core and removing the defective portions thereof by means of a suitable cutting tool.
U.S. Pat. No. 4,288,907 discloses a method of making billets whereby a composite billet is produced by continuous casting or rolling. The billet is formed as having a star-shaped cross-section with a central portion and ray members disposed symmetrically to the central longitudinal axis of the billet. The "pipe" or segregation zone of the billet is caused to be concentrated within the central portion such that the ray members may be severed therefrom. The reference further describes another method of making billets involving separating the billet in the direction of its length into two or three sections that allows the area of axial segregation to be removed by planing.
U.S. Pat. No. 4,196,505 discloses a method of making fuel injection pipes from a steel bar material. A pipe body is formed by cutting and removing an interposed slag layer that is collected and deposited along the longitudinal axis of the bar. The pipe body so formed then is elongated to the desired dimensions.
As to the general manufacture of branch connectors and similar fittings, U.S. Pat. No. 1,860,605 discloses a method of forming tube fittings for hydraulic brake systems. The fittings are machined from severed sections of a solid metal bar or rod.
U.S. Pat. No. 2,165,454 discloses a method of fabricating T-fittings from a preformed metal rod that eliminates certain drilling and machining operations. A section of the rod is severed to having a cubic content corresponding to that of the fitting. The section then is cold-worked within a punch and die assembly into the desired fitting configuration.
U.S. Pat. No. 3,740,813 discloses a method of making a pressure pipe connector tee of a relatively large size and wall thickness. A solid metal workpiece is heated to forging temperature, peripherally confined within a die, and then hollow punched to provide a selected wall portion that is sufficiently thick to permit the formation of branch pipe passages therein.
U.S. Pat. No. 3,961,513 discloses a method of making a tee-shaped pipe fitting. A solid plug of malleable metal is deformed to provide a closed-end tube having a thicker wall portion adjacent the closed end. The tube then is further deformed to provide a pair of legs adjacent the closed end.
The above-referenced methodologies heretofore have constituted the state of the art with respect to the manufacture of branch connectors and other fittings of the type herein involved. It will be appreciated, however, that continued improvements in such methodologies would be well-received by industry in general, and especially those industries such as the semiconductor industries having applications which dictate miniaturized fittings of high integrity. Preferred methods would allow for the economical manufacture of such fittings, while assuring a negligible rejection rate.